Programmed cell death in yeast by thionin-like peptide from fruits involving activation of caspases and extracellular H flux.

Thi is a thionin-like peptide isolated from fruits of , which has strong antimicrobial activity against bacteria, yeasts and filamentous fungi, and induced reactive oxygen species (ROS) in fungi. ROS are molecules that appear in the early stages of programmed cell death or apoptosis in fungi. Due to this fact, in this work we analyzed some events that may be related to process of apoptosis on yeast induced by Thi. To investigate this possibility, we evaluated phosphatidylserine (PS) externalization, presence of active caspases and the ability of Thi to bind to DNA in cells. Additionally, we investigated mitochondrial membrane potential, cell surface pH, and extracellular H fluxes in cells after treatment with Thi. Our results showed that Thi induced PS externalization in the outer leaflet of the cell membrane, activation of caspases, and it had the ability for DNA binding and to dissipate mitochondrial membrane potential. In addition, the cell surface pH increased significantly when the cells were exposed to Thi which corroborates with ~96% inhibition on extracellular H efflux. Taking together, these data suggest that this peptide is capable of promoting an imbalance in pH homeostasis during yeast cell death playing a modulatory role in the H transport systems. In conclusion, our results strongly indicated that Thi triggers apoptosis in cells, involving a pH signaling mechanism.